Overhead power grid for mobile mining machines

ABSTRACT

A vehicle is provided that connects to an power structure for powering and guiding the vehicle. The power structure includes a trolley, a track along which the trolley runs, a power source connected to the track, and a cable connected to the trolley and configured to attach to the vehicle moving on a surface. The vehicle includes a chassis and a cable connected to the chassis and configured to mechanically and electrically connect the vehicle to the power structure. The chassis includes a connector rotatable 360 degrees, and the cable connects to the chassis through the connector.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/738,378, filed Jun. 12, 2015, which is acontinuation-in-part of U.S. patent application Ser. No. 13/755,239,filed Jan. 31, 2013, which claims priority to U.S. Provisional PatentApplication No. 61/593,073, filed Jan. 31, 2012. The entire contents anddisclosure of these documents are incorporated by reference herein.

BACKGROUND

The present invention relates to movable electric machinery, and, moreparticularly, to a power grid connected to movable electric machinery.

Heavy mining machinery used in surface mining and underground “hardrock” mining is typically powered by diesel engines. There has long beena need to reduce the health risks associated with operating such dieselengines in confined surface and underground mining applications.Specifically, diesel engines emit particulate matter harmful to humans,create high noise levels, and add significantly to the “heat loading” inan underground mine. Additionally, the high cost of diesel fuel anddiesel engine maintenance present additional downsides.

Conventional overhead grid powered systems, such as rail transportationsystems, use pantographs that slide on an overhead wire. These systemsrequire the use of rail based guidance to keep the movable machine(locomotive) within an acceptable proximity to the overhead wires(conductors). Pantograph systems have been attempted to be implementedwith haul trucks, but such pantograph systems do not include any“switching” means to switch the direction of travel along the roadway orrail other than lowering the pantograph, going back on diesel power tomake the turn, and then re-engaging the pantograph to get back onoverhead power.

SUMMARY

According to an embodiment of the invention, a power structure isprovided for powering and guiding a vehicle. The power structureincludes a trolley, a plurality of generally tubular and parallelsegments forming a track along which the trolley runs, a power sourceconnected to the tubular segments, and a cable connected to the trolleyand configured to attach to a vehicle moving on a surface. The cablemechanically and electrically connects the vehicle to the trolley.

According to another embodiment of the invention, a vehicle isconfigured to connect to a power structure. The vehicle includes achassis and a cable connected to the chassis and configured tomechanically and electrically connect the vehicle to the powerstructure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top perspective view of a mobile mining machine connected toa power grid according to an embodiment of the invention.

FIG. 2A is a partial right side perspective view of the mobile miningmachine connected to the power grid of FIG. 1.

FIG. 2B is a plan view of a special connector for the mobile miningmachine of FIG.

1.

FIG. 2C is a perspective view of an alternative embodiment of the mobilemining machine.

FIG. 3A is a perspective view of a trolley for the power grid accordingto another embodiment of the invention.

FIG. 3B is a plan view of FIG. 3A.

FIG. 4 is an exploded plan view of the power grid.

FIG. 5 is a perspective view of the power grid including a switchmechanism.

FIG. 6 is an overhead plan view of an alternative embodiment of thepower grid in a turning configuration.

FIG. 7 is a perspective view of FIG. 6.

FIG. 8 is an overhead plan view of the alternative embodiment of thepower grid of FIG. 6 in a straight configuration.

FIG. 9 is a perspective view of FIG. 8.

FIG. 10A is a plan view of a power grid according to another embodiment.

FIG. 10B is a plan view of the power grid shown in FIG. 10A in a firststate.

FIG. 10C is a plan view of the power grid shown in FIG. 10A in a secondstate.

FIG. 10D is a plan view of the power grid shown in FIG. 10A in a thirdstate.

FIG. 11 is a perspective view of a portion of the power grid of FIGS.10A-D.

FIG. 12 is an enlarged perspective view of a portion of the power gridof FIG. 11.

DETAILED DESCRIPTION

Before any embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangement of components set forthin the following description or illustrated in the following drawings.The invention is capable of other embodiments and of being practiced orof being carried out in various ways. Also, it is to be understood thatthe phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising” or “having” and variations thereof herein ismeant to encompass the items listed thereafter and equivalents thereofas well as additional items. The terms “mounted,” “connected” and“coupled” are used broadly and encompass both direct and indirectmounting, connecting and coupling. Further, “connected” and “coupled”are not restricted to physical or mechanical connections or couplings,and can include electrical connections or couplings, whether direct orindirect. Also, electronic communications and notifications may beperformed using any known means including direct connections, wirelessconnections, etc.

FIGS. 1 and 2 illustrate a mobile mining machine 100 (such as aload-haul-dump vehicle, hereinafter “LHD”) mining operations. The LHD100 is electrically and mechanically connected to a power structure 1(e.g., an overhead power structure) via a trolley 10. The overhead powerstructure 1 may be a free standing structure or may be suspended from aceiling of a mine.

As shown in FIGS. 2A and 3, the overhead power structure 1 includes aplurality of generally tubular conductors 2 and rail segments 3. Theouter tubes are rail segments 3 along which guide wheels 11 of thetrolley 10 run, and the inner tubes are metallic conductor tubes 2 thatform the conductors for a 3-phase AC power grid 20. The power grid 20may be of multiple types, i.e. AC, DC, AC 3-phase, etc. The metallicconductor tubes 2 may be formed of copper or another conductive metal.The conductors 2 and rail segments 3 form a power grid structure 1 thatis connected to the LHD 100 by a trailing cable 110.

As shown in FIGS. 2A and 3, the trailing cable 110 hangs down from thetrolley 10 and connects the power from the power grid 20 to the LHD 100.The trailing cable 110, along with the associated trolley 10 and specialconnector 120 (further discussed below) on the LHD 100 keeps the groundor floor surface of the mine free of cables so other equipment can bemore easily operated, especially other tetherless equipment.

As best viewed in FIG. 2B, the trailing cable 110 connects to thechassis 101 of the LHD 100 through a special connector 120 rotatable 360degrees. The special connector 120 allows the trailing cable 110 to besafely removed without harm to the LHD 100, trolley 10, power structure1, or mining personnel. The connector 120 includes a spring-loaded ball121 that works in a detent 122 to hold the trailing cable 110 in asocket 123. However, with enough pull, the trailing cable 110 can bepulled out from the connector 120. The ability of the trailing cable 110to easily release from the connector 120 is important in case thetrolley 10 gets hung up, and to prevent pulling down the overhead gridsegments 2, 3 in case the LHD 100 travels beyond the reach of the cable110.

In an alternative embodiment, in addition to or instead of allowing thetrailing cable 110 to release from the connector 120 in the event of amalfunction, the trolley 10 includes a control means to de-energize thepower through the cable 110 to the LHD 100. The control means caninclude a circuit breaker, a control transformer, a contactor, a groundfault interrupter, or a logic controller mounted on the trolley. Thecontrol means may also include an angle or tension sensor that indicatesa position or angle of the trailing cable 110 (i.e. that the cable 110is not hanging substantially vertically or being pulled at some angleexceeding a pre-determined threshold angle). If the sensor determinesthe angle of the cable 110 exceeds the minimum threshold angle, thecontrol means signals a cable reel 130 (further described below) to payout additional cable 110 or signals the operator to apply the brakes tothe LHD 100. If there is no cable reel 130 or if the cable 110 in thecable reel 130 has reached its maximum output, an additional ripcord maybe attached between a chassis of the LHD 100 and a base of the trolley10 to indicate that the cable 110 is at a maximum tension, thus alteringthe operator to apply the brakes. Additionally, the circuit breaker or agrounding circuit of the power structure 1 may cut off power to the grid1 in the event of tension in the cable 110 reaching a second, higherthreshold.

As shown in FIG. 2C and as discussed above, the LHD 100 may include acable reel that stores the trailing cable 110. The presence of the cablereel 130 allows the LHD 100 to move across larger distances, while stillremaining connected to the overhead power structure 1. For example, thetrailing cable 110 is long enough for the LHD 100 to reach into otherentries far enough to load ore, or perform other required tasks, whilestaying connected to the overhead power grid 1 and not getting tangledup in itself. The cable reel 130 may be attached anywhere on the LHD orHaul Truck, such as the front side shown in FIG. 2C. The cable 110 isfed from the reel 130 through a vertical extension conduit 131 coupledto the cable reel 130. An upper portion of the conduit 131 is secured tothe connector 120, preferably at a height approximately slightly belowthat of the conductors 2 and rail segments 3 of the overhead powerstructure 1 to minimize interference of the trailing cable 110 withother components or operators of the LHD 110. However, the conduit 131may have other heights as desired for various operations.

As discussed above, the LHD 100 connects to the power structure 1 viathe trolley 10 that runs along the rail segments 3 and that commutateswith the power structure 1. As shown in FIGS. 3A-3B, the trolley 10includes a base 12 that runs below and generally parallel to theoverhead power structure 1. Two flanges 13 rise upwards from respectivelateral sides of the base 12 on the outside of the rail segments 3. Apair of spaced upper guide wheels 11 a and a lower guide wheel 11 b aresecured to an inner side of each flange 13. However, the number andspacing of the upper 11 a and lower 11 b guide wheels may be varied. Thelower guide wheels 11 b cooperate with the upper guide wheels 11 a to“squeeze” the rail segments 3 to ensure the trolley 10 remains properlybalanced on the rail segments 3 and so that commutators 15 (furtherdiscussed below) remain properly aligned with the conductors 2.

With continued reference to FIG. 3A and 3B, the trolley includescommutators 15 that connect to the grid conductors 2 via a commutationmaterial such as graphite. The trailing cable 110 then connects thecommutators 15 to the LHD 100. The commutators 15 may include agrounding circuit from the LHD 100, that extends through ground leads inthe trailing cable 110, and then through the trolley wheels 11 that rideon the outer rails 3 of the overhead grid 1. A “universal joint” swivel16 is disposed on the base 12 of the trolley 10 and a cable clamp 17 isused to secure the trailing cable 110 to the trolley 10. The trailingcable 110 hangs down from the clamp 17 and connects to the connector 120mounted on the LHD 100.

As shown in FIGS. 4 and 5, embodiments of the present invention alsoinclude a switch device 30 to allow movement from one mine entry toanother. With reference to the plan view of FIG. 4, because the overheadgrid segments 2, 3 include multiple conductors 2 (three are shown inFIG. 4) in between two outer tubular rail segments 3, the segments A, B,C may be mechanically moved into place. Segment A is slidable to theright and left in the direction of the arrows shown in the drawing inthe plan view of FIG. 4 to create a straight portion of the switch 30.Segments B and C slide back and forth “over” the main track lines at a45 degree angle (in the direction of the corresponding arrows shown inthe drawing) and then drop down into position to form a right or leftturn as the trolley 10 approaches from the right in FIG. 4.

In the embodiment shown in FIG. 5, movements are carried out by a winch40 that lowers the individual segments into place. However, themovements of the segments can be carried out with slides, cams, linearactuators, belts, or other devices known in the art. A controller (notshown) may be utilized to electronically control the mechanicalactuation of the segments A, B, C. A device similar to the switch device30 could be utilized for the LHD 100 to pass another mining machine,provided enough room exists in an underground or surface passageway.

In an alternative embodiment, instead of having a separate mechanism forthe respective segments of track to be switched into place, a turntable50, shown in FIGS. 6-9, performs the switching of the pieces of track.The turntable 50 includes a generally circular outer ring 51 and asupport member 52 connected to and extending between the ring 51. Thesupport member 52 connects the ring 51 to a straight rail segment and/ora curved rail segment. The support member 52 shown in FIGS. 6-9 has agenerally rectangular shape, with arc-shaped longitudinal end sides 53,the arc-shaped end sides 53 mating with the ring 51. The support member52 includes a base member 54 disposed thereon so that the turntable 50may be suspended from a ceiling.

The turntable 50 is rotatable to align either the curved rail segment inorder for the LHD 100 to make a right or left turn (FIGS. 6-7) or toalign the straight rail segment with the fixed portions of the track inorder for the LHD 100 to move straight (FIGS. 8-9). The turntable 50could be modified to be used in a 4-way intersection, if necessary. Acontroller (not shown) having a motor position sensor or the like may beused to control rotation of the turntable.

In operation, as the LHD 100 moves along entryways in an undergroundmine, or along dedicated roadways on a surface mine, the trailing cable110 pulls the trolley 10 along the overhead power grid system 1, thusmaintaining connectivity to the power grid 20. The LHD 100 can moveabout and turn completely around in a circle without the trailing cable110 binding or touching the ground. The connection to the mining machine100 includes a “breakaway” connector 120 in case the LHD 100 tries tomove further than a maximum distance the trailing cable 110 will allow.The mobile mining machine 100 would then be able to move about theentries in an underground mine by “towing” its trolley 10 behind, whiledrawing power from the overhead grid structure 1.

The overhead power grid 1 for mobile mining machines 100 according toembodiments of the present invention utilizes electric-powered miningmachines 100 in surface and underground mines without the use ofground-engaging trailing cables and/or cable reels. The typical trailingcable with a cable reel wears out quickly and hinders the passage ofmultiple cable-reel powered machines (which cannot drive over energizedcables). The overhead grid system 1 eliminates this gridlock scenario byproviding switches 30 and intersections where machines may pass eachother. For instance, if two LHD's 100 approach the intersection depictedin FIG. 3, one from the bottom of the figure and one from the right sideof the figure, and both attempt to head towards the top of the figure,one of the LHD's 100 can stop, wait for the other to pass through theintersection, and then continue behind the first. If these miningvehicles used “lay-down” trailing cables via a machine-mounted cablereel, the second LHD 100 would have to wait for the first 100 to returnand pass back through the switch in the direction it originally camefrom before the second LHD 100 could proceed towards a position at thetop of the figure.

The overhead power grid 1 for mobile mining machines 100 offerssignificant health and safety advantages over diesel power machines byreducing or totally eliminating the dependence on diesel power, as allof the machines connected to the grid would be electrically powered, forexample, via a Variable Frequency Drive (VFD) and/or a SwitchedReluctance Drive (SRD). Utilizing these electronic drive technologies inconjunction with the overhead power grid 1 also offers the advantage ofgreater power when needed and the ability to “regenerate” braking powerback into the grid, thus optimizing energy efficiencies. Regeneration isthe process of using the electric wheel motors as generators to convertthe energy of deceleration (braking) and turn it back into the samevoltage and frequency to pump it back on the grid 1.

FIGS. 10A-D illustrate a power grid according to another embodiment. Thepower grid 20 is a 3-phase AC power supply and includes a firstconductor 202, second conductor 203, and third conductor 204. Eachconductor carries an AC current of the same frequency and voltage, witha phase difference. For example, the first conductor 202 conveyselectrical current having a first phase, the second conductor 203conveys the same electrical current as the first conductor 202 buthaving a second phase, and the third conductor 204 conveys the sameelectrical current as the other conductor but having a third phase. Thecurrent in each conductor is out of phase with each other conductor.

The power grid 20 also includes a switch device 230 to allow a vehicleto move from one mine entry to another. The switch device may permit thevehicle and trolley as described above to move between a primary track210 and an auxiliary track 220 via switch segments A, B, and C. In theexemplary construction, illustrated in FIGS. 10B and 10C, each conductor202, 203, 204 of the primary track 210 is aligned with a correspondingconductor 202, 203, 204 of the switch. Stated another way, the firstconductor 202 of the switch segment A is connected to and associatedwith the first conductor 202 of the primary track 210, the secondconductor 203 of the switch segment A is connected to and associatedwith the second conductor 203 of the primary track 210, and the thirdconductor 204 of switch segment A is connected to and associated withthe third conductor of the primary track 210. In addition, eachconductor 202, 203, 204 of the switch segments are connected to thecorresponding conductor of the output or destination track (e.g., thelower end of the primary track 210 in FIG. 10B, and the auxiliary track220 in FIG. 10C). The properly aligned conductors 202, 203, 204 allowthe trolley 10 (FIG. 2A) to move sequentially from one track section toanother track section while maintaining proper electrical communicationwith each conductor 202, 203, 204, thereby allowing the machine to movebetween mine entries.

Referring to FIG. 10D, the conductors 202, 203, 204 of the switch device230 may become misaligned with the conductors of the primary track 210in some configurations. In the illustrated example, the first conductor202 of the auxiliary track 220 is connected to the third conductor 204of the lower end of the primary track 210. The electrical currentcarried by each conductor is therefore out-of-phase between the switchsegment C and the primary track 210, which could damage the line andpose a safety hazard.

As shown in FIGS. 11 and 12, the end of each conductor 202, 203, 204 ofthe auxiliary track 220 is coupled to a transition member or connectormember 205. In one embodiment, each connector member 205 is made from anon-conducting material (e.g., plastic). In other embodiments, theconnector members 205 may be formed integrally with one another. Whenthe trolley 10 passes over the connector members 205, the contacts ofthe trolley pass through a “dead zone” in which no current istransmitted through the contacts. This dead zone allows the electricalcurrent to “reset” or to be re-conditioned to accept current from theconductors from the switch segment C that the trolley 10 contacts next,even if the conductors 202, 203, 204 have a different phaseconfiguration. The “reset” may occur as the trolley is disconnected fromthe power (e.g., comes into contact with the connector member 205). Eventhough the power supply to the vehicle may be interrupted, the motion ofthe trolley and the vehicle provides sufficient inertia to move thetrolley over the connector 205 and into engagement with the next sectionof the conductors 202, 203, 204.

In other embodiments, the connectors 205 may be secured to theconductors on the switch segment instead of or in addition to beingsecured to the track 220. Furthermore, each end of the conductors on theprimary track 210, the auxiliary track 220, and the switch segments A,B, and C may include a connector 205. The connector may be coupled toone or more ends of the switch, one or more ends of the primary track210, and/or one or more ends of the auxiliary track 220, or anycombination thereof

In another construction, the engagement of the trolley 10 with theconnectors 205 may create a signal (e.g., via wireless communication) tothe trolley 10 to prepare for a switch in the phase of the AC currentsupplied by each conductor 202, 203, 204. In yet another construction,the engagement between the trolley 10 and the connector 205 may signal amechanical switch element on the trolley 10 to maintain contact with thesame phase conductor 202, 203, 204. Each of these embodiments isexemplary by nature, and other suitable switch mechanisms, bothmechanical and electrical, may be used.

In operation, the switch device 30 utilizes an actuator to move switchsegments A, B, C generally along the directions of the arrows shown inFIGS. 10A-10D into and out of alignment with primary track 210 to allowthe LHD vehicle to selectively move between primary track 210 andauxiliary track 220. When switching from track to another track, thenon-conducting connector 205 accounts for any phase difference in in thecurrent or voltage carried by conductors 202, 203, 204, resetting thetrolley to accept the phase configuration of the track toward which thetrolley 10 is travelling.

Although the invention has been described in detail with reference tocertain preferred embodiments, variations and modifications exist withinthe scope and spirit of one or more independent aspects of the inventionas described.

What is claimed is:
 1. A system for providing electrical power to avehicle, the system comprising: a first track including a firstconducting portion carrying a current having a first phaseconfiguration; a second track including a second conducting portioncarrying a current having a second phase configuration different fromthe first phase configuration; a trolley movable sequentially along thefirst track and the second track, the trolley including a contact, thecontact in electrical communication with the first conducting portionwhile the trolley moves along the first track, the contact in electricalcommunication with the second conducting portion while the trolley movesalong the second track, the contact conditioned to receive currenthaving the first phase configuration while the contact is in electricalcommunication with the first conducting portion; and a connectorpositioned between the first conducting portion and the secondconducting portion, wherein when the contact of the trolley engages theconnector, the contact is conditioned to receive current having thesecond phase configuration when the contact is positioned in electricalcommunication with the second conducting portion.
 2. The system of claim1, wherein the second track is removably coupled to the first track by aswitch device.
 3. The system of claim 2, further comprising a thirdtrack supported on the switch device, the third track including a thirdconducting portion, wherein the first track is selectively coupled tothe third track.
 4. The system of claim 1, wherein the connector isformed from an electrically non-conductive material.
 5. The system ofclaim 1, wherein the connector is secured to an end of the firstconducting portion.
 6. The system of claim 1, wherein when the contactof the trolley engages the connector, the contact is reset such that thecontact is conditioned to receive electrical current from the secondconducting portion when the contact subsequently engages the secondconducting portion.
 7. The system of claim 1, wherein the firstconducting portion includes a first conductor, a second conductor, and athird conductor, the first conductor carrying current having a firstphase, the second conductor carrying current having a second phase, thethird conductor carrying current having a third phase, wherein thetrolley includes a first contact engaging the first conductor, a secondcontact engaging the second conductor, and a third contact engaging thethird conductor, wherein the second conducting portion includes a firstconductor, a second conductor, and a third conductor.
 8. The system ofclaim 7, wherein the connector includes a first member, a second member,and a third member, the first member positioned between the firstconductor of the first conducting portion and the first conductor of thesecond conducting portion, the second member positioned between thesecond conductor of the first conducting portion and the secondconductor of the second conducting portion, the third member positionedbetween the third conductor of the first conducting portion and thethird conductor of the second conducting portion.
 9. A power structurefor a vehicle, the power structure comprising: a first track portionincluding a plurality of first electrical conductors, each of theplurality of first electrical conductors including a first end; a secondtrack portion including a plurality of second electrical conductors,each of the plurality of second electrical conductors including a secondend; and a plurality of connectors, each of the plurality of connectorsdisposed on at least one of the first end of the first electricalconductors and the second end of the second electrical conductors, eachof the plurality of connectors being electrically non-conductive suchthat the connectors form a dead zone between the first electricalconductors and the second electrical conductors.
 10. The power structureof claim 9, further comprising an actuator for moving the second trackportion relative to the first track portion to selectively form acontinuous path between the first track portion and the second trackportion.
 11. The power structure of claim 10, further comprising a thirdtrack portion including a plurality of third electrical conductors, eachof the plurality of third electrical conductors including a third end; asecond actuator for moving the third track portion to selectively form acontinuous path between the third track portion and one of the firsttrack portion and the second track portion; and a plurality ofconnectors, each of the plurality of connectors disposed on third end ofthe third electrical conductors, each of the plurality of connectorsbeing electrically non-conductive.
 12. The power structure of claim 10,wherein the actuator displaces the segments along a generally linearpath.
 13. The power structure of claim 9, wherein the plurality of firstelectrical conductors receive a first electrical current from a firstthree-phase alternating current source, the first electrical conductorsincluding three conduits, the first electrical current having a firstphase configuration such that a current in each of the three conduits isapproximately 120 degrees out of phase with the current in each of theother conduits.
 14. The power structure of claim 13, wherein theplurality of second electrical conductors receive a second electricalcurrent from a second three-phase alternating current source, the secondelectrical conductors including three conduits, the second electricalcurrent having a second phase configuration that is different from thefirst phase configuration, wherein a current in each of the threeconduits of the second electrical conductors is out of phase with thecurrent in the associated conduits of the first electrical conductors.15. The power structure of claim 9, wherein the first track portion andthe second track portion are aligned with one another in an end-to-endrelationship, wherein each of the plurality of connectors is positioneddirectly between the first end of one of the plurality of firstconductors and the second end of one of the plurality of secondconductors.
 16. A power structure for a vehicle, the power structurecomprising: a first track portion including a plurality of firstelectrical conductors, each of the plurality of first electricalconductors including a first end; a second track portion including aplurality of second electrical conductors, each of the plurality ofsecond electrical conductors including a second end; and a plurality ofconnectors, each of the plurality of connectors disposed on at least oneof the first end of the first electrical conductors and the second endof the second electrical conductors, each of the plurality of connectorsbeing electrically non-conductive such that the connectors form a deadzone between the first electrical conductors and the second electricalconductors, wherein the plurality of first electrical conductors receivea first electrical current from a first three-phase alternating currentsource, the first electrical conductors including three conduits, thefirst electrical current having a first phase configuration such that acurrent in each of the three conduits is approximately 120 degrees outof phase with the current in each of the other conduits.
 17. The powerstructure of claim 16, further comprising an actuator for moving thesecond track portion relative to the first track portion to selectivelyform a continuous path between the first track portion and the secondtrack portion.
 18. The power structure of claim 16, further comprising athird track portion including a plurality of third electricalconductors, each of the plurality of third electrical conductorsincluding a third end; a second actuator for moving the third trackportion to selectively form a continuous path between the third trackportion and one of the first track portion and the second track portion;and a plurality of connectors, each of the plurality of connectorsdisposed on third end of the third electrical conductors, each of theplurality of connectors being electrically non-conductive.
 19. The powerstructure of claim 16, wherein the actuator displaces the segments alonga generally linear path.
 20. The power structure of claim 19, whereinthe plurality of second electrical conductors receive a secondelectrical current from a second three-phase alternating current source,the second electrical conductors including three conduits, the secondelectrical current having a second phase configuration that is differentfrom the first phase configuration, wherein a current in each of thethree conduits of the second electrical conductors is out of phase withthe current in the associated conduits of the first electricalconductors.